MacroLogos
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This should help with the difference between a fan/propeller blade that uses an 'airfoil' design vs an 'airscrew' design.So you don't find a fan blade with a "foil" design (similar to how modern sail boats use air flowing over a sail's surfface to "pull" the boat, rather than using it to "push" it, and air plains use this same principle in wing design to create lift), to be creating a vacuum?
The filters level of pressure drop is the same be it on the suction side or the discharge side of the fan. That number does not change, a pressure drop is a pressure drop. How the fan reacts to the pressure drop is what's important. If on the suction side the fans performance is gutted because the fan and housing can not be loaded properly. If the filter is on the discharge side of the fan and the suction side is open with no more restriction than the tent vent panels present then the fan blade and housing can load up properly and make cfm and discharge pressure. With the fan loaded properly the fan can make better discharge pressure to combat the pressure drop restriction of the filter. Most of the company's suggest the filter on the suction side for ease of use,,, plain and simple. Some will show discharge into the filter as a secondary way of setup. But never truly touch on the sizing, pressure drop. Remember your garden is not producing stale air. Your plants are feeding on CO2 in your air and making O2. They are scrubbing and filtering the air. Is it dramatic? No, but that is what they are doing. In my setup the return air filter and duct is a foot away from the door of my office. So any humidity that is exhausted from the grow space is going right into the central A/C and improving the A/C units wet bulb performance a small amount. So outside the A/C unit is pissing like a race horse on a flat rock and maintaining a perfect RH for the wife and I in the home at around 40% and have a very good temp differential of 20 to 21F degrees. That means I have 70F air hitting the return air filter and the A/C is putting out 50F air at a central located register. With the evap coil pissing the condensate out of the unit,,, ie: dehumidification the condensate is carrying away impurities in the air as the water catches them and they flow out of the unit into one of the wifes flower gardens.
Thanks! Great vid!
This is the best information in a video I have seen, and should help with this discussion.
Good vid, but there is some deeper science at play worth looking at... if you're into this stuff.
This is the best information in a video I have seen, and should help with this discussion.
Great vid also! So going by what I've just seen the optimal setup would be to filter on exhaust side and add a lip on the fan housing input side that will give the Coranda effect which will decrease strain on the motor and help in air flow as the effect is drawing air in naturally aside from the mechanical draw the fan is making?Good vid, but there is some deeper science at play worth looking at... if you're into this stuff.
This guy does a couple other vids, but the intro is going to give solid insight into this topic.
A pressure drop is a pressure drop be it on the suction or discharge of the fan, blower or pump. It is a constant. The only thing that changes is how dirty the filter gets and increasing the pressure drop. Prefilters are to protect the filter from mechanical filtration and dirting up the carbon and they have there own pressure drop. I always rinse my carbon filter before use. I don't understand what your questions are and how they truly apply to the issue at hand. A fan, blower or pump makes differential pressure. If you rob the fan of supply air because of a pressure drop on the suction side it will never meet or make as much cfm or discharge pressure. If we leave the suction side open and allow the fan to load properly it will make much better cfm and discharge pressure. If we block the suction side of the fan we are throwing it right into a Low NPSH situation. ( Net Positive Suction Head ) which destroys the performance of said fan, blower or pump. Do the hand experiment I posted about earlier in this thread.Curious.......you say that fan performance is degraded because of filter restriction on the frontside(input air) causing improper fan load. Most modern a/c's use a filter front design which would be in conflict to what you are saying would optimize fan performance. Is the difference the filter media that is being used in relation to the fan CFM being employed on that particular design? In another thread front side filtering was mentioned as a way to keep fan components cleaner. True or not?
Also, you say that with the input side unloaded, other than tent vents, the fan can load properly but you also say that pressure drop is the same be it suction or discharge with the same filter on either end. I'm assuming your increase in fan performance is what is yielding you the better discharge numbers. In essence the higher flow rates will flow more out of the filter. What I don't get is if the filter media has a flow limit how can the increased performance of the fan surpass that limit? Are you saying that the lower performance of , say an ACI T6 unit since you mentioned ACI fans, doesn't push the filter to its limit thus lowering net cfm? Because the filter is not being pushed to its CFM limits would the fan performance not match whatever level the filter is allowing it to flow on the frontside/input side of the fan vs being used on the discharge side? I'm sure there are some physics and aero laws that would explain this but I'm curious about your explanation and how that works.
BTW did you rinse your filters before hooking them up to mitigate carbon dust? I know you used the prefilter inside the chamber but putting it on the outside, IMO, would be better to keep carbon dust from escaping into the atmosphere. Prefilter on the inside or outside should have no difference in relation to airflow but I could be wrong.
ALSO, LOL, since we're on the subject of airflow, when in flower, to keep the girls in total darkness I have to cover my vent panels. I have two 6" vents that I plan on using as my input air but I need to connect a length of flex duct to kill whatever light is entering. I tested the airflow, no instrument testing just SOP testing by how much negative pressure the tent was under through visual. How do I calculate how much vent area I need to properly supply the tent and fan? I have an ACI T6 unit in the vent and am thinking of using your setup of filter on the discharge end.
Optimal is subjective...Great vid also! So going by what I've just seen the optimal setup would be to filter on exhaust side and add a lip on the fan housing input side that will give the Coranda effect which will decrease strain on the motor and help in air flow as the effect is drawing air in naturally aside from the mechanical draw the fan is making?
I guess I'm confusing air pressure and air volume. If the filter is physically blocking the volume of air that can be pulled through the filter why would it be any different on the exhaust side? The physical limit has been reached in regards to how much air can flow through the filter.A pressure drop is a pressure drop be it on the suction or discharge of the fan, blower or pump. It is a constant. The only thing that changes is how dirty the filter gets and increasing the pressure drop. Prefilters are to protect the filter from mechanical filtration and dirting up the carbon and they have there own pressure drop. I always rinse my carbon filter before use. I don't understand what your questions are and how they truly apply to the issue at hand. A fan, blower or pump makes differential pressure. If you rob the fan of supply air because of a pressure drop on the suction side it will never meet or make as much cfm or discharge pressure. If we leave the suction side open and allow the fan to load properly it will make much better cfm and discharge pressure. If we block the suction side of the fan we are throwing it right into a Low NPSH situation. ( Net Positive Suction Head ) which destroys the performance of said fan, blower or pump. Do the hand experiment I posted about earlier in this thread.
One can not exist without the other. Look at the fan and pump curve I posted. Has head pressure goes up flow goes down. The point of no flow is max head pressure. The point of max flow is zero head pressure.I guess I'm confusing air pressure and air volume. If the filter is physically blocking the volume of air that can be pulled through the filter why would it be any different on the exhaust side? The physical limit has been reached in regards to how much air can flow through the filter.
I get that the air pressure drop is hurting the fans overall performance through different physical effects(bernoulli, etc.) but to what effect? 10% loss? 80% loss?
You're the expert. I'm not doubting your knowledge. Just trying to get a better grasp so that I can build a more efficient exhaust system that can better control temp and humidity.
Air pressure (- or +) determines how quickly air will move through the filter.If the filter is physically blocking the volume of air that can be pulled through the filter why would it be any different on the exhaust side? The physical limit has been reached in regards to how much air can flow through the filter.
I run 6" systems on my 2x4 and 3x3 both tents 95" tall. If I was to go to a 4x4 or 5x5 the regardless of height I would move right up to a 8" setup. You never want to be in a position to where you have to run your exhaust fans wide open full tilt boogie. Each tent has a 6" x 12" intake mesh panel and I never run my fans above speed 6 maybe 7. So I never have issue with not removing odor and maintain humidity and temp just fine.So if we extrapolate both, the pressure the fan will build is really what determines how much volume will move through the fan itself minus whatever restrictions like ducting/filters etc. hence why, in your experience and through measurements, doing it this way will yield a better air exchange rate within the tent itself.
Now......the reason people use charcoal filters is usually to mitigate smell. Air speed dictated by air pressure will dictate how effective the filter will be at reducing the smell since faster speed means less time the air has to interact with the activated charcoal or is this nominal within the scheme of things? Yes, people use them for both, this guy included, so I'm trying to find the balance between odor mitigation and temp/humidity control. Lower air speed, i.e. air pressure will help with odor mitigation while higher air speed will help in temp/humidity control. That is what I'm getting from this. The issue at hand is that when odor mitigation is needed so is a higher air exchange rate since more transpiration and more intense lighting in flower will raise both.
I'll ask again, how much vent do I need to properly vent a 5 x 5 x 80" tent if I set up the filter on exhaust and leave the input in open air meaning no curved edge for the Corana effect?
Logical and will add it to my knowledge base so that the next time I set up a tent I have a better understanding in how to size my ventilation.I run 6" systems on my 2x4 and 3x3 both tents 95" tall. If I was to go to a 4x4 or 5x5 the regardless of height I would move right up to a 8" setup. You never want to be in a position to where you have to run your exhaust fans wide open full tilt boogie. Each tent has a 6" x 12" intake mesh panel and I never run my fans above speed 6 maybe 7. So I never have issue with not removing odor and maintain humidity and temp just fine.
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